7/16-14 UNC tap drill size
Use a letter U drill (0.3680 in, 9.35 mm) for 7/16-14 UNC. It is the standard chart size and leaves about 75% thread, enough for full practical strength without excessive tapping torque.
| Drill | inch | mm | Thread % | Typical use |
|---|---|---|---|---|
| T | 0.3580 | 9.09 | 85.7% | Tight: high tapping torque, tap breakage risk |
| 23/64" | 0.3594 | 9.13 | 84.2% | General purpose |
| 9.3 mm (metric drill) | 0.3661 | 9.3 | 76.9% | General purpose |
| U (chart drill) | 0.3680 | 9.35 | 74.9% | General purpose |
| 3/8" | 0.3750 | 9.52 | 67.4% | Hard or tough material, deep or blind holes |
| V | 0.3770 | 9.58 | 65.2% | Hard or tough material, deep or blind holes |
| W | 0.3860 | 9.8 | 55.5% | Low engagement: check strength |
| Thread | Tap drill | Tap drill (mm) | Clearance close / free |
|---|---|---|---|
| 5/16-18 UNC | F (0.2570 in) | 6.53 mm | P / Q |
| 3/8-16 UNC | 5/16" (0.3125 in) | 7.94 mm | W / X |
| 7/16-14 UNC (this page) | U (0.3680 in) | 9.35 mm | 29/64" / 15/32" |
| 1/2-13 UNC | 27/64" (0.4219 in) | 10.72 mm | 33/64" / 17/32" |
| 9/16-12 UNC | 31/64" (0.4844 in) | 12.3 mm | 37/64" / 19/32" |
Practical notes
Spiral-point taps suit through holes; spiral-flute taps lift chips out of blind holes. In a blind hole, drill a few threads deeper than the full-thread depth you need.
Typical engagement lengths: about 1 × diameter in steel, 1.5 × in cast iron or brass and 2 × in aluminium. In tough stainless or hardened steel a slightly larger drill (60–70% thread) cuts torque and tap breakage with little loss of strength.
Thread-forming (roll) taps need a larger hole, roughly 0.4018 in (10.21 mm, D − 0.5 × pitch). Check the tap maker's chart; forming suits ductile metals such as aluminium, mild steel and brass, not cast iron.
UNC (coarse) is the default Unified series: quicker to assemble, more tolerant of dirt and damage, and better in soft materials such as aluminium and cast iron.
Clearance drills for a 7/16 screw: close fit 29/64" (0.4531 in, 11.51 mm), free fit 15/32" (0.4688 in, 11.91 mm).
FAQ
What size drill for a 7/16-14 UNC tap?
The standard tap drill for 7/16-14 UNC is a letter U drill, 0.3680 in (9.35 mm), which gives about 75% thread.
What clearance hole for a 7/16 UNC screw?
Use 29/64" (0.4531 in, 11.51 mm) for a close fit or 15/32" (0.4688 in, 11.91 mm) for a free fit. Clearance depends on diameter only, so it is the same for UNC and UNF 7/16 screws.
What metric drill can I use for 7/16-14 UNC?
The closest metric drill is 9.3 mm (0.3661 in), giving about 77% thread on 7/16-14 UNC.
What is the difference between 7/16-14 UNC and 7/16-20 UNF?
Both are 7/16 diameter. 7/16-14 UNC has 14 threads per inch and uses a U tap drill (0.3680 in); 7/16-20 UNF has 20 TPI and uses a 25/64" drill (0.3906 in). The threads are not interchangeable.
Sources: ASME B1.1 — Unified inch screw threads (UN and UNR form) · Machinery's Handbook — tap drill sizes and percentage-of-thread formula · ASME B94.11M — twist drills (number and letter drill sizes) · Common machinist clearance-drill chart (close / free fit)
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